QUESTIONS AND ANSWERS 17 



What is combustion? 



Combustion is rapid oxidation and is accompanied by heat and 

 light. 



Distinguish between, an oxidizing and a reducing agent and give an 

 example of each. 



An oxidizing agent is one which readily parts with its oxygen 

 when brought in contact with substances having a greater affinity 

 for it. Example : KCIO3. 



A reducing agent is one which has the power to abstract oxygen 

 from an oxide. Example : hydrogen. 



What is meant by (a) slow oxidation, (b) rapid oxidation? Give an 

 example of each. 



(a) A process of oxidation evolving no light. Example : oxida- 

 tion of the different organic substances in the living body. 



(b) When the heat generated by oxidation is sufficient to cause 

 the emission of light and perhaps a loud report, the process is called 

 rapid oxidation, or combustion. Example: gunpowder is a mix- 

 ture of sulphur, carbon and potassium, KNO3. Upon heating or ignit- 

 ing this mixture, the sulphur and carbon are oxidized, and various 

 gases (CO, COj, N, SO2, etc.) are formed, the sudden generation 

 and expansion of which cause the explosion. 



Describe a method of preparing oxygen on a commercial scale. Write 

 the equation to express the reaction. 



Heat to redness in an iron vessel manganese dioxide (MnOj), 

 causing it to decompose into manganous manganic oxide and oxygen. 

 SMnO^ = MugO^ + 20. 



Compare the physical and chemical properties of oxygen with those 

 of hydrogen. 

 Both gases are colorless, odorless and tasteless. Oxygen is 16 

 times heavier than hydrogen. Oxygen supports combustion but is 

 non-combustible, whereas hydrogen is combustible but not a sup- 

 porter of combustion. 



What is ozone? Describe the preparation of ozone. 



Ozone is an allotropie modification of oxygen. It possesses 

 a peculiar odor and is a stronger oxidizing agent than common oxy- 

 gen. Its symbol is O3. 



Ozone is prepared by passing non-linninous electric discharges 

 through atmospheric air or through oxygen. 



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